test: delete test-infrastructure dead code (G)

- exit-propagation drives the runner's real strict verdict
  (BunTestOutputClassifier + strictTestExitCode); delete the unused
  shardRunLooksTruncated predicate.
- delete skill-coverage-matrix registry + its gate (nothing reads it; the
  floor already iterates skillCensus()).
- delete touchfiles-facade export-parity tests (Bun fails missing imports
  at link time) and the duplicated E2E_TIERS tier-value test.
- delete brain-cache-spec TRANSPORT_DEFAULT_POLICY, SKILL_RUN_RETENTION_DAYS
  and the now-unused BrainTrustPolicy type with their literal tests.
  AUTOPLAN_PREFLIGHT_BUDGET_BYTES stays: skill-preflight-budget enforces it
  against real resolver output.
- delete audit-compliance's JSDoc-comment grep.

scripts/brain-cache-spec.ts

@@ -162,12 +162,6 @@ export const SKILL_CALIBRATION_WEIGHTS: Record<string, number> = {
  */
 export const CACHE_REFRESH_LOCK_TIMEOUT_MS = 5 * 60_000;
 
-/**
- * Retention policy: gstack/skill-run pages auto-archive after this many days.
- * Calibration takes (kind=bet) NEVER archive (long-term scorecard needs them).
- */
-export const SKILL_RUN_RETENTION_DAYS = 90;
-
 /**
  * Schema pack identity. Bumped when adding/removing/renaming page types.
  * On mismatch with the version recorded in _meta.json, the cache layer
@@ -176,26 +170,6 @@ export const SKILL_RUN_RETENTION_DAYS = 90;
 export const GSTACK_SCHEMA_PACK_NAME = 'gstack-core';
 export const GSTACK_SCHEMA_PACK_VERSION = '1.0.0';
 
-/**
- * Trust policy values. Drives auto-push of artifacts, calibration write-back
- * eligibility, and user-namespacing strategy.
- */
-export type BrainTrustPolicy = 'personal' | 'shared' | 'unset';
-
-/**
- * Per-transport default policy. Local engines auto-set to personal (single-tenant
- * by construction). Remote endpoints are inferred based on sources_list shape:
- * exactly one source + whoami matches → personal default; multiple sources or
- * federation → ask the policy question.
- */
-export const TRANSPORT_DEFAULT_POLICY: Record<string, BrainTrustPolicy | 'infer'> = {
-  'local-pglite': 'personal',
-  'local-stdio': 'personal',
-  'remote-http-single-tenant': 'personal',
-  'remote-http-ambiguous': 'unset',
-  unknown: 'unset',
-};
-
 /**
  * User-slug fallback chain (D4 A3 defensive default). Resolved once per endpoint
  * and persisted via `gstack-config set user_slug_at_<endpoint-hash> <slug>`.